A. Field of the Invention
The present invention relates generally to voice over packet based networks, and more particularly, to SIP communication networks.
B. Description of Related Art
The transmission of voice and video over packet based networks, as compared to traditional dedicated line telephone service, provides the possibility of significantly cheaper and more flexible voice and video connectivity.
SIP (session initiation protocol) is a signaling protocol for initiating, managing and terminating voice and video sessions across packet networks. SIP sessions involve one or more participants and can use unicast or multicast communication. Borrowing from ubiquitous Internet protocols, such as HTTP and SMTP, SIP is text-encoded and highly extensible. SIP may be extended to accommodate features and services such as call control services, mobility, and interoperability with existing telephony systems.
Conventionally, in SIP, mechanisms exist for performing a call transfer. In a call transfer, a first party (e.g., party A) and a second party (party B) are engaged in a communication session. A call transfer occurs when party A instructs the system to terminate party A's call with party B and instead connect party B to a third party (e.g., party C). A receptionist, for example, may frequently wish to transfer an incoming caller's call to an appropriate final recipient for the call.
The conventional SIP protocol enables rudimentary call transfers but does not address the proper billing of a transferred call nor the prevention of unwanted call transfers or fraudulent activities related to transfers.
In accordance with a traditional approach, if party B calls party A and then party A causes party B to be transferred to party C, then party B is viewed as the originator of the call to party C and any charges are assessed to party B. However in some instances, when party A transfers party B to party C, it may be desirable to bill party A rather than party B. For example, party A and party C may be phones within a business enterprise, and party B may be a customer who calls party A seeking service. Party A may need to transfer the inbound call to party C. If there are extra charges involved in connecting the call to party C, it may be desirable that the business enterprise be assessed any such charges rather than having the customer, party B, pay for the transferred call.
An unwanted call transfer may relate to party A being unauthorized to perform a transfer. For example, party A may be a telephone in an unsecured area such as the lobby of a corporate office or a hotel.
Without proper controls, such a phone may be a springboard for penetrating a company's phone system or for placing fraudulent toll calls that will be billed to the phone.
Another form of unwanted call transfer may arise when party B is normally disallowed from calling party C directly, perhaps for reasons of security or because of call charges. It may be desirable in some circumstances to ensure that party A does not, intentionally or unintentionally, circumvent the restrictions configured into the network that otherwise prevent party B from reaching party C. As a form of fraud, party B may try to deceive party A into completing the call to party C, perhaps causing charges to be assessed to party A. Of course, it is also conceivable that, in some situations, party A might be given the authority to transfer party B to party C, even if party B cannot reach party C directly. For example, a receptionist may transfer an inbound call to a doctor, even if the doctor's line cannot be reached directly by callers outside the office.
Exposure to fraud arises when party B is able to capture signaling information during a successful transfer to party C by party A. During the transfer, party B may obtain enough information from the conventional SIP messages to be able to reproduce similar signaling later and subsequently contact party C without going through party A. This is another technique by which party B may conduct fraudulent or unwanted communications. For example, party B may “replay” the signaling information to make it appear that party A should pay for subsequent calls.
Accordingly, there is a need in the art to improve call transfer support under the SIP protocol.